Monitoring a biological state of a driver during driving is gaining attention in recent is years as an accident prevention measure or the like. The present applicant has hitherto proposed various such techniques. Patent Document 1 discloses an apparatus having a procedure to obtain a time series waveform of a frequency mainly from a time series waveform of a biosignal which is cardiocirculatory pulsation sampled from an upper body of a person, further obtain a time series waveform of a frequency gradient and a time series waveform of a frequency fluctuation, and frequency-analyze them. When performing a frequency analysis, power spectra of respective frequencies corresponding to a function adjusting signal, a fatigue reception signal and an activity adjusting signal belonging in a ULF band (ultra low frequency band) to a VLF band (very low frequency band), which are predefined, are obtained. Then, the state of the person is determined from time series changes of the respective power spectra. The fatigue reception signal indicates the degree of progress of fatigue in a normal active state, and thus by comparing, together with this, the degrees of predominance of the power spectra of the function adjusting signal and the activity adjusting signal, the state of the person (relaxed state, fatigue state, sympathetic nerve predominant state, parasympathetic nerve predominant state, or the like) can be determined.
Patent Document 2 uses, similarly to Patent Document 1, the function adjusting signal, the fatigue reception signal and the activity adjusting signal belonging in the ULF band (ultra low frequency band) to the VLF band (very low frequency band), but Patent Document 2 is of a method obtaining, in time series, distribution rates of respective frequency components when a total of values of power spectra of the frequency components corresponding to the three signals is 100, and determining the state of a person by using time series changes in the distribution rates.
The techniques of Patent Documents 1 and 2 are both based on knowledge as follows. Specifically, human homeostasis is retained by fluctuation, and its frequency band is regarded to be in the ULF band and the VLF band. On the other hand, in atrial fibrillation as one of heat diseases, it is said that the point where a characteristic of fluctuation of the heart-circulatory system switches is 0.0033 Hz, and by grasping a change in fluctuation in the vicinity of 0.0033 Hz, information related to homeostasis can be obtained. Further, it is said that frequency bands in the vicinity of 0.0033 Hz or lower and in the vicinity of 0.0053 Hz are mainly related to body temperature adjustment, and the frequency band of 0.01 to 0.04 Hz is said to be related to control of autonomic nervous system. Then, when a frequency gradient time series waveform for calculating these fluctuations of low frequencies which are inherent in the biosignal was actually obtained and subjected to frequency analysis, it was confirmed that there were fluctuations of frequency band around 0.0017 Hz which is a lower frequency than 0.0033 Hz and 0.0035 Hz in the vicinity of 0.0033 Hz, and a fluctuation of frequency band around 0.0053 Hz besides these two.
The signal of 0.0035 Hz (fatigue reception signal) is a fluctuation for maintaining homeostasis by adapting to externally inputted stress, and this is a signal indicating the degree of progress of fatigue in a normal active state, the signal of 0.0053 Hz (activity adjusting signal) is a signal in which the degree of influence by control of endocrine hormones in an active time appears, the signal of 0.0017 Hz (function adjusting signal) which is a lower frequency than 0.0033 Hz is a signal controlling modulation and/or functional decrease of a body, and the signals of these three frequency bands are correlated one another to function as a body temperature adjusting function. Then, time series changes of power spectra and distribution rates of these signals are used for determining the state of a person.